Coded track circuit with means to neutralize the inductive kickback from track rails



M. A. SCHEG CUIT W Sept. 8, 1953 CODED TRACK CIR ITH MEANS TO NEUTRALIZE THE INDUCTIVE KICKBACK FROM TRACK RAILS Filed Dec. 22, 1949 Patented Sept. 8, 1953 CODED TRACK CIRCUIT WITH MEANS TO NEUTRALIZE THE INDUCTIVE KICKBACK FROM TRACK RAILS Marcian A. Scheg, Rochester, N. Y., assignor to I(general Railway Signal Company, Rochester,

Application December 22, 1949, Serial No. 134,407

Claims.

This invention relates to coded track circuits, and more particularly pertains to an improved organization for transmitting and receiving code pulses in such a track circuit.

The most common practice in connection with coded track circuits is to provide a code transmitter relay at each end of a track section, the code transmitter relay at one end operating its contacts at different selected code rates to alternately connect a source of energy and a code following track relay across the track rails at that end of the track section to transmit a driven code. At the other end of the track section the code transmitter relay is normally inactive and connects the associated code following track relay across the track rails, but upon the reception of a driven code pulse, the track relay is actuated and in turn momentarily actuates the associated code transmitter relay to eliect the connection of a source of energy across the track section to transmit an inverse code pulse to the track relay which is then connected to the other end of the track section. In this way, driven code pulses and inverse code pulses are transmitted in opposite directions alternately through the track section. The contacts which apply the sources of energy across the track section have relatively large currents to make and break when the ballast between the track rails is Wet and of a relatively low resistance value. Also, when a train shunts a track section, the inverse code pulses are of course not transmitted, but the coding contacts at the leaving end of the track section continue their operation and must make and break still larger values of track current.

In view of the above considerations, it has been proposed in the prior application of W. H. Reichard, Ser. No. 623,220, filed October 19, 1945, to feed code pulses to the track section from a source of alternating current through step-down transformers and rectifierswith the coding operation being effected by contacts of the code transmitter relay included in the high side of the step-clownv transformer. In this way, the current required to be broken by the contacts is reduced in accordance with the ratio of the stepdown transformer and at the same time the voltages involved are increased. Such an organization then permits relatively hard contact materials, such as tungsten, to be employed.

It is further proposed in such above mentioned prior application that the code following track relays be directly connected across the track rails, and that they be of a polarized type 'of relay connected with such a polarity as to be unresponsive to the polarity of the code pulses applied at their respective ends of the track secion. t 1

It is to be understood that the present inven tion should be considered as an improvement over the type of coded track circuit organization shown in said prior application, Ser. No. 623,223 (now Pat. No. 2,588,044, dated March 4, 1952), and that no claim is made in this application to any subject matter disclosed in such prior application.

When coded track circuits of the type just described are used with track ballast of relatively low resistance, the ballast itself acts as leakage to the inductive currents produced by the code pulses in the track rails; but, when the ballas is dry and there are no such leakage paths, the end of each transmitted code pulse is followed by an inductive kick-back current from the track rails of such a polarity that it tends to improperly operate the associated track relay which is permanently connected across the rails. This is especially objectionable where follow-up code transmitting means is employed as in connection with highway crossing signals and the like, since it would be possible under some circumstances to obtain a false clearing of a signal.

In view of the above considerations, it is proposed in accordance with the present invention to provide the transmitting and receiving organization at the signal end of the track section with suitable means for neutralizing the eiTect of the inductive kick-back current from the track rails. More specifically, and without attempting to define the exact nature of the invention, it is proposed to use an inductive reactance in the local transmitting circuits in such a way that its reactive currents will combine with the inductive kick-back currents from the track rails at the end of each code pulse transmitted to neutralize the effect on the associated track relay. The use of such an inductive reactance in the combination contemplated by the present invention has been found to not only prevent improper response of the associated track relay during the transmission of inverse and follow-up codes, but it has also been found useful for improving the response of the associated code following track relay in connection with the reception of driven codes from the opposite end of the track section.

Other objects, purposes, and characteristic features of the present invention will be in part obvious from the accompanying drawing, and in part pointed out as the description of the invention progresses.

In describing the invention in detail, reference will be made to the accompanying drawing which shows a typical application of the present invention to a coded track circuit involving a highway crossing.

In the drawing, corresponding letter reference characters are used to designate corresponding parts or devices having similar features and functions, with such letter reference characters being generally made distinctive by reason of succeeding numerals. In describing the invention, reference may be made from time to time to functions common to all parts of a similar character by use of the like letters common to such parts without the numerals characteristic of the locations or devices with which the respective parts are associated.

For the purpose of simplifying the illustration of this embodiment of the present invention and faciliating in the explanation thereof, various parts and circuits have been shown diagrammatically rather than showing the specific construction and arrangement of parts that would be employed in practice. The various relays and their contacts are illustrated in a conventional manner and symbols are used to indicate connections to the terminals of batteries or other sources of electric current instead of showing all of the wiring connections to these terminals. For convenience in simplifying the drawings, certain of the relays have been shown in block form without detailed control circuits, it being understood that their control may be accomplished in any suitable and conventional manner as well known in the art.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries, and the circuits with which these symbols are used always have current flowing in the same direction. The symbols (BX) and (CX) are used to indicate the opposite terminals of a suitable alternating current source.

System apparatus With reference to the single drawing, a stretch of track including track sections Tl, T2, T3, and Ti, suitably insulated from each other, have been shown as typical of any such stretch employed along the railroad. A signal S2 is shown at the v entrance of the track section T2 and a signal S4 is shown at the entrance of track section T4, it being assumed that these signals S2 and S4 are properly spaced for a block signalling system but that the track circuit between them has to be broken up to provide signalling facilities for a highway which intersects the railroad. Adjacent the highway are suitable warning signals designated HS which are controlled by the usual interlocking relay XR, such as shown, for example, in Pat. No. 1,824,131, dated September 22, 1931, and which in turn is controlled by the coded track circuit apparatus as hereinafter pointed out.

At the exit end of the block and adjacent the signal St, a transformer 6 is supplied with alternating current from the terminals BX and CK through a front contact 1 of a code transmitting relay CP l in accordance with the particular code then to be applied to the track section. This relay CP t is a code transmitting relay which is controlled in accordance with traffie conditions in such a way as to operate at the proper code rate depending upon the conditions of traffic conditions in section T4. Ordinarily, this relay would be caused to operate at a 180 code rate (180 pulses per minute) if the next track section T4 in advance is unoccupied but would be caused to operate at a '75 code rate if such next section T4 were occupied by a train. The solid arrow, according to the drawing, is indicative of the direction of driven code transmission, while the dashed arrow is indicative of the direction of inverse code transmission.

This application of alternating current to the primary winding of transformer 6 causes halfcycles of alternating current to be applied across the track rails of section T3 through half wave rectifier 8. Since transformer S is a step-down transformer, the code pulses are formed by the coding contact I in a circuit which has a relatively high potential so that the contact I may be made of tungsten or a like hard contact material. On the other hand, the voltage in the secondary circuit of transformer 63 is relatively low so as to supply the proper amount of current to the track circuit including the track rails of section T3 and a track relay TBS at the opposite end of this track section. At the leaving end of the track section T2, 2. similar transformer Q, and rectifier [0 are controlled by the coding contact ll of the track relay TPUS so as to repeat the code pulses from the tracl: section T3 into the track section T2. At the entrance end to the track section T2, a track relay TREE is provided to receive the driven code pulses and to operate in accordance with the code transmitted from the exit end of the block adjacent the signal 84.

The tracl: r lay TRZ has associated therewith slightly slow-acting repeater relay TP2 which is controlled through a front contact I2 so as to be picked up whenever a code pulse is received to be dropped away at, a predetermined time after the end of that code pulse. This time of drop away for this relay TPZ is properly selected so as to represent the proper length of an inverse code pulse which may be transmitted between ai" two successive driven code pulses. Thus, the back contact [3 of track relay TRZ and the front contact ll of this repeater relay TP'Z, act at the end of each driven code pulse to energize the primary winding of the transformer 15 for the proper time to transmit an inverse code pulse.

This transformer i5. is a step-down transformor the same as the transformer 6, but its secondary winding is connected to a full wave rectifier R2 which is connected across the rails of track section T2 through an inductive reactor 1N2. Thus, following the reception of each driven code pulse, an inverse code pulse of rectified alternating current is applied to the track rails of section T2. This inverse code pulse is received by the approach relay APUZ adjacent the highway crossing which operates its coding contact IE to repeat the inverse code pulse into the track secon T3. The closure of contact It applies alternating current to the primary winding of the transformer i"? which is similar to the transformers 8, 9, and i5 and which has its secondary winding connected across the track rails through the full wave rectifier R3 and the inductor 1N3. The repeated inverse code pulses on track section T3 are received by the approach relay AR3.

It should be understood that the track relays TR2, T33, and the like, along with the approach relays ARZ, A113, and the like, are preferably of the polarized type, i. e., respond to only a particular polarity of current. For convenience in the illustration, these relays are assumed to respond only to current flowing through their windings in the direction indicated by the arrows.

The track relay TRZ acts through suitable decoding means, one'typical form being shown, to

control the signal S2 to indicate clear, caution, or stop. When a 180 code is received, the decoding apparatus acts to energize both relays H2 and D2 causing the signal S2 to indicate green or clear providing the relay API is deenergizeddue to the approach of a train. When a 75 code is received, the decoding apparatus acts to energize only the home relay H2 to cause the signal S2 to indicate yellow or caution providing, of course, that the approach relay AP! is dropped away. Whenever the track relay TRZ is not operated, the decoding apparatus is so constructed as to assume an inactive condition and cause the signal S2 to indicate red or stop. The control of each signal may be direct, or it may be approach controlled as shown. The approach relay API is controlled the same as relay AP3 which is operated by inverse codes in a manner to complete the circuit for energizing the associated signal only when no inverse code is being received. In

other words, the cessation of the inverse code which normally pulses the relay AR-B causes the dropping away of relay AP3 by the opening of its circuit in an obvious manner. The dropping away of relay A1 3 applies energy to signal S4 in the same mamier as the dropping away of relay AP! applies energy selectively to the lamps of signal S2. Specifically, these approach relays AP are slow acting relays which maintain their contacts picked up only so long as code pulses are received, and have back contacts for approach lighting the associated signals. This has merely been indicated in connection with the approach relay AP3, rather than showing all of the details of such circuit.

Associated with the signal S2 are coding contacts l8 which operate at any suitable rate. Although this rate may be 75 pulses per minute, so as to employ contacts on the same code oscillators as required for signal codes at a signal location, any other suitable rate adapted for transmitting follow-up codes may be used. Thus, when the track section T2 has no driven code pulses therein, the repeating relay TP2 remains dropped away and the home relay H2 is also dropped away closing back contact is which allows the coding contacts I8 to intermittently energize the primary winding of the transformer 15. This causes a followup code to be applied to the track section T2 to maintain the highway crossing signal inactive although a train is still occupying the track section T3. This is so that the highway crossing signals HS may be allowed to indicate clear for the highway as soon as the rear end of a train has passed the insulated joints adjacent the highway.

The approach track relay AR2 at the highway crossing operates in response to both inverse and follow-up codes. This operation is effective to maintain the approach relay APZ picked up so long as codes are received, due to the intermittent energization of relay APZ through front con tact 22. But when codes are not received by relay ARZ, the relay APE is continuously deenergized and drops away opening its front contact 23 to effect the operation of the highway crossing signal through deenergization of the left-hand winding of interlocking relay XR. This, of course, happens when a train passes the signal S2.

In the same manner, the relay TP3 is maintained energized by its intermittent energization through front contact 2c of relay T33 in response vto the receptionof driven code pulses. Whenever 6 the section T3 is occupied and the relay TEE fails to receive code pulses, then the relay TF3 drops away opening front contact 29 and deenergizing the right-hand winding of the interlocking relay XR.

In connection with the interlocking relay XR, it may be understood that the first winding deenergized has its back contact closed but the second winding to be deenergized cannot close its back contact because of mechanical means set into position by the deenergization of the first winding to prevent such closure. Thus, the reenergization of the first winding to have been deenergized stops the crossing signal because the interlocking means is not restored until the second winding to be deenergized has been reenergized. In this Way a highway crossing signal is caused to be effective for a train approaching in either direction but is rendered inactive as soon as that train passes beyond the highway.

It is believed that further understanding of the invention will be best obtained by a consideration of the operation of the system.

Operation Under normal conditions, a driven code is applied to the track section T3 by reason of the operation of the coding relay CPi. In other words, code pulses are successively applied to the track section T3 by closure of front contact 7 with the approach track relay AR3 being connected to the rails between each pair of pulses. The application of a driven code pulse is repeated by the picking up of track relay TRB which closed contact H applying a driven code pulse to the track section T2 which in turn is repeated by the track relay TRE. This driven code pulse is maintained for a sufficient period to pick up the relay TF2.

The removal of such driven code pulse results in the successive release of the track relays TR3 and TRZ. The opening of front contact i2 deenergizes repeater relay TF2 which drops away after a short time period. Back contact ll; becoming closed completes an energizing circuit through front contact M of relay TF2 for the transformer i5 during the drop away period of this relay TP2. This causes an inverse code pulse to be applied by the transformer and rectifier combination to the track section TE. This pulse is received by the track relay ARE, because back contact 2c is closed at this time. The closure of the front contact it causes an inverse code pulse to be applied to the track section T3 which energizes the approach track relay ARE because back contact 2i of code transmitting relay SP is closed at this time. The inverse code pulse is, of course, temporary because the relay TP2 releases after a short interval. Thus, the relays AR2 and ARE are restored to deenergized conditions by the time the code transmitting relay CP i is again energized for transmitting a driven code pulse.

In this way, driven code pulses and inverse code pulses are alternately transmitted in opposite directions through the track sections T2 and T3 being repeated at the insulated joints adjacent the highway crossing by the relays AR2 and TR3. It will be noted that each driven code pulse is made up of half wave rectified alternating current, while each inverse code pulse is made up of full wave rectified alternating current. The half wave rectified alternating current is :preferably used for driven code pulses so as toprovide pulses of a character adapted to be picked up by cab signals of train control apparatus. Also, these driven code pulse are preferably separated by off periods substantially equal to the duration of the pulses. In other words, the driven code is preferably made of substantially equal on and ofi periods. This is desirable so as to provide pulses at the receiving end of the track section which may be most efficiently decoded for the control of the signal governing relays.

With such equal on and off periods, it will be apparent that the inverse code pulses must be shorter than the oii periods in order to fit into the time allotted with suitable margins. Since the inverse code pulses are thus shorter than the driven code pulses, it is desirable to provide full wave rectified alternating current pulses for the inverse code in order to transmit suificient energy to the opposite end of the track section for the operation of the track relay at that end.

It will be noted that the track relay TR3 is directly connected across the track rails without any commutating contacts. Likewise, the full wave rectifier R3 is connected directly across the track rails through the inductance 1N3 without any commutating contacts. Each driven code pulse is of such a polarity that it may be properly received by the track relay TR? to cause its operation. This polarity corresponds to the rectifier R3 polarity so that the driven code pulse would ordinarily be short circuited by the rectifier unit R3 except for the resistance of the rectifier and the leads connecting the rectifier across the track rails. This circuit might have resistance added in order to provide a greater voltage drop for the relay TBS, but this would render the transmitting organization less efficient. However, the inclusion of the inductive reactan-ce 1N3 in the output circuit of the rectifier unit R3 causes this shorting circuit to oppose the buildup of a driven code pulse at its leading edge so that the track relay TR3 is caused to quickly respond to such driven code pulse. In this way, the rectifier unit R3 may be employed without having adverse effect upon the response of the track relay TBS.

The reception of a driven code pulse by track relay TR3 causes it to be repeated into track section T2; and the response of track relay TRZ and its associated circuits and apparatus causes the transmission of an inverse code pulse which momentarily energizes relay ARZ. This momentarily closes contact [6 to momentarily energize the primary winding of the transformer ll and cause an inverse code pulse to be applied across the track rails T3 of a proper polarity to cause the relay ABS to respond, but this polarity is not the polarity to cause the response of the track relay TR3. When the inverse code pulse is removed by thev opening of front contact IS, the current from thispulse must die out in the track rails, but under some circumstances this current is of such a large value that the inductive characteristic of the rails becomes great and tends to maintain such current by reason of the leakage through the ballast and thus produces a voltage at points 2-5 and 2B of such a polarity as to improperly actuate the track relay TR3. Thus, if the ballast conditions are such as to permit little, or no, leakage through the ballast, it may happen that this inductive voltage appearing across points 2-5 and 26 will be suiliciently high to cause the improper operation or" the track relay TR3. Obviously, it is not proper to have the track relay TR3 respond to inverse code pulses.

The present invention prevents this improper response because the current of the inverse code pulse has also been flowing through the inductive reactance 1N3, so that this inductive reactance 1N3 upon the interruption of the primary winding at contact [6 tends to create a potential at points 25 and 26 opposite to the potnetial produced at those points by the inductive reactance of the track rails upon the cessation of such inverse code pulse. The inductive reactance 1N3 is so selected that the potential produced by it is substantially equal to the potential produced by the inductive reactance of the rails. Since these potentials are thus substantially equal and opposite. there is no net difference in potential between the points 25 and 26 to act upon the track relay TR3. In this way, the inductive reactants of the track rails is balanced or neutralized to thereby prevent improper operation of the track relay T33. In other words, the pulse current flowing through the inductance IN3 and the track rails is in the same direction so that the interruption of the current supply results in an inductive current tending to flow in the same direction as the inverse code pulse current. This inductive current is in eifect the result of two inductive sources which are on opposite sides of the track relay connection. For this reason, the track relay is connected at what may be termed a neutral point in the circuit having the circulating inductive current. Thus, it may be said that the inductive currents are balanced or neutralized in their effect with respect to the track relay PR3 by the provision of the inductive reactors IN.

It is noted that the same operations and functions take place in connection with the inductive reactance IN2 at the signal location S2. In the drawing, the inductive reactance IN2 is shown in the positive output lead of the rectifier R2, whereas, the inductive. reactance 1N3 is shown in the negative lead of the rectifier R3. This illustrates that the inductive reactance may be located in either the positive or negative lead of the rectifier connection, since its function is the same in both cases. This is because the current flow through the associated rectifier always ineludes the inductive reactance.

In addition, at the signal location S2, follow up codes are applied when a train is occupying either or both of the track sections T2 and T3. Thus, for each closure of the coding connection 8, a follow-up code pulse is applied to the rails of track section T2; and at the end of each such follow-up code pulse, the inductive reactance of the track rails of section T2 cause potentials at points 21 and 28 of such a polarity as to tend to improperly actuate the track relay TRZ. More specifically, if the track relay PR2 should be improperly operated With a train shunting track section T2, the relay H2 would be picked up opening back contact 19 to stop the transmission of the follow-up codes. This would stop the improper operation of track relay TR2 and after an interval of time relay H2 would release. This operation would repeatedly occur so that the signal S2 would be cleared improperly at intervals while a train was in the track section T2. However, the present invention obviates this improper operation because the inductive reactance IN2 at the end of each follow-up code pulse, as well as at the end of each inverse code pulse, produces a potential across the points 2'] and 28 equal and the end of a follow-up code pulse will be stronger when a train is occupying the section T2 near its exit end, it should be appreciated that the presence of a train in section T3 causes a followup code to be transmitted and the inductive kickback potentials in track section T2 may still be substantial in spite of the resistance of the approach relay ARZ included in the track circuit.

In addition, it shoold be noted that with the can in track section T3 the follow-up codes are likecrossing the same as inverse code pulses. Thus, if the follow-up code pulses in track section T3 should cause suflicient inductive kick-back potentials with a train in that section, the track relay TR3 would be improperly operated (if inductance INS were not employed) and would cause the transmission of pulses in the track section T2 to improperly operate the track relay TR2. Obviously, the track relay TR2 could not distinguish between such improper pulses and the pulses of a regular driven code. Thus, the apparatus located at signal 552 would cause inverse code pulses to be transmitted in place of the follow-up code pulses, so that the continuance of an improper operation of the track relay TRB by reason of inductive kick-back potentials in track section T3, would establish a condition for the continuous transmission of erroneous codes and the false clearing of signal S2 while the track section T3 is occupied. It can thus be seen that the provision of the inductances INZ and INS provide important protection against improper signal operation due 'to inductive kick back potentials where follow-up codes are used in connection with highway crossing systems.

It should be noted that the inductive current in the track rails at the end of an inverse code pulse is of such a polarity that it merely continues the actuation of the approach relay at the opposite end of the track section (AR2 for example), and no improper operation occurs. If the inverse code pulse is prolonged unduly by the inductive. eifect of the rails, then the operation of the code transmitter GP for the next driven code pulse will open back contact 2!) for example and interrupt the circuit for the relay ARZ so that it is assured of dropping away. The same operation occurs with respect to the approach relay AR3.

In the above discussion, it was pointed out that the inductive kick-back currents at the end of inverse code pulses might operate the track relays, but if driven code pulses were being received to cause such inverse code pulses, the improper opwise repeated into that section past the highway eration of the track relay under such circumbe made into a track section where inverse codes are being transmitted and this might result in the self-coding of the local track relay by the inverse code transmitting apparatus, under the conditions of ballast where the inductive kickback currents are the most troublesome. This is pointed out so as to show that the characteristic features of the present invention should be applied to track circuits of the type disclosed herein regardless of whether they are associated with highway crossing control or not.

Referring to the drawing, it will be noted that the application of an inverse code pulse for operating the relay AR2 is of the proper polarity to be passed by a circuit including the secondary winding of the transformer 9 and the rectifier is. But the inductive 'reactance of the transformer serves to provide impedance to such inverse code pulse so that it may quickly and effectively actuate the track relay ARE as intended in spite of the presenc of such circuit. It might also be pointed out in this connection that the transmission of a driven code pulse by the closure of front contact H results in an inductive kick-back in the rails which might erroneously operate the relay ARE under some circumstances, but the transit time of the contact 2e subsequent to the opening of front contact I! is suflicient to allow the inductive kickback currents to substantially decay before the relay ARZ is connected across the track rails.

Having described a coded track circuit organization as one specific embodiment of the present invention, it is desired to be understood that this particular form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and it is to be further understood that various adaptations, alterations, and modifications may be applied to the specific form shown to meet the requirement of practice without in any manner departing from the spirit or scope of th invention.

What I claim is:

1 In a coded track circuit organization for railroads, a section of railway track having driven code pulses applied thereto at one end of .a rate dependent upon traffic conditions, a polarized track relay permanently connected across the track rails at the other end, a rectifier unit, an inductive reactor connected in a circuit including said rectifier across the track rails in multiple with said track relay at saidotherend, circuit means governed by said track relay for applying inverse code pulses across said rectifier to transmit them through said inductive reactor and said track rails in series, and inverse code receiving means at said one end of said track section.

2. In a coded track circuit organization for railroads, a section of track, driven code transmitting means and inverse code receiving means both located at one end of said track section and alternately acting to transmit driven code pulses and receive inverse code pulses between successive pairs of driven code pulses, a rectifier unit having an input circuit and an output circuit located at the other end of said track section, an inductive reactor having an inductance comparable to the inductance of the track rails of said section, circuit means connecting said inductor in series with the output circuit of said rectifier across the track rails of said section at its other end, a track relay of the polarized type connected across said track rails of said section with such a relative polarity as'to be-unresponsive to energy applied to the track *rails from the output of said rectifier, and circuit means controlled by contacts ,of said track relay operating in response to the reception of a driven code pulse for causing the momentary application of alternating current to the input circuitof said rectifier unit, whereby said track relay is protected against improper operation by inductive kick-back currents from said rails upon the transmission of inverse ,COdE pulses due to the neutralizing efiect of said inductive reactor.

3. In a coded track circuit for a section of railway track, a source of alternating current at each end of the section, a code transmitter at each end of the section and each having contacts of relatively hard contact material, a stepdown transformer located at each end of the track section and each having primary and secondary windings, circuit means at each end of the section including wire connections and a rectifier for permanently connecting the secondary winding of the associated transformer across the track rails at its end of the track section, said connections at opposite ends being of opposite polarity, and said connection at one end including an inductive reactor, circuit means at the other end of said track section including contacts of the associated transmitter for intermittently connecting the source of alternating current at that end to the primary winding of the associated transformer at a rate selected in accordance with traffic conditions, a relay at said other end connected so as to be responsive only to pulses in the track rails between successive energizations of said primary winding at that end, a polarized relay at said one end of said section directly and permanently connected across the track rails but with its polar connections being opposite to the polarity of the associated rectifier at that end, and circuit means controlled by said polar relay following its response to each pulse received over the track rails for momentarily energizing said code transmitter relay at that end for momentarily connecting the associated source of alternating current to the primary winding of said transformer at that end, whereby inverse and driven code pulses are alternately transmitted and whereby said polarized track relay is protected against operation by inductive currents in the track rails at the end of the inverse code pulses, but is rendered more quickly responsive to the driven code pulses since said inductive reactor provides an impedance in the output circuit or said rectifier unit.

4. In a coded track circuit organization for railroads, a section of railway track having driven code pulses applied thereto at one end of a rate dependent upon trafiic conditions, a polarized track relay permanently connected across the track rails at the other end, a full wave rectifier unit having an input circuit and an output circuit, an inductive reactor connected in the output circuit of said rectifier and across the track rails in multiple with said track relay, circuit means governed by said track relay for applying inverse code pulses to the input circuit of said rectifier to transmit them through said inductive reactor and said track rails in series, and inverse code receiving means at said one end of said track section.

5. In a coded track circuit organization for railroads, a section of track having driven code pulses applied thereto at one end, a polarized track relay permanently connected across the track rails at the other end and responsive to said driven code pulses, circuit means including an inductive reactor and a source of energy governed by said track relay for transmitting inverse code pulses over said rails through a circuit connection including said reactor in series with said source and the rail current, said circuit connection being made across said track rails in multiple with said polarized track relay and with such a polarity that the inverse code pulses fail to cause the operation of said polarized track relay, whereby said reactor and the track rails provide additive inductive potentials upon the interruption of the rail current at the end of each inverse code pulse which inductive potentials are ineffective to acuate said polarized track relay since its connection is at neutral points with respect to said inductive potentials,

MARCIAN A. SCHEG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,609,140 Thompson Nov. 80, 1926 1,754,592 Beall Apr. 15, 1930 2,001,047 Witmer May 14, 1935 2,184,877 Shields Dec. 26, 1939 2,328,241 Wight Aug. 31, 1943 2,399,760 Rees May 7, 1946 2,515,642 Gilson July 18, 1950 2,588,044 Reichard Mar. 4. 1952 

